Various types of threads used in the oilfield tubular business have beneficial properties. U.S. Pat. No. 1,932,427 discloses a pipe joint with buttress threads. U.S. Pat. No. 2,006,520 discloses a casing joint with substantially square threads having flanks substantially perpendicular to the axis of the connection.
The threaded pipe connection of the present invention relates to threads which use tapered stepped first and second threads on the ends of the connected tubulars. The first tapered thread is axially spaced from and has a different nominal diameter than a second taped thread on the same tubular. U.S. Pat. No. 4,537,429 discloses a tubular connection with tapered and stepped threads.
Many threaded connections include some type of nose or load shoulder for engagement with a stop surface on the opposing connection to limit the rotation and thus the axial position of the connected tubulars. Wedge threads avoid the requirement for a shoulder, since the varying width of the wedge thread replaces the nose end or shoulder to limit rotation and thus axial position of the connected tubulars.
U.S. Pat. No. 4,671,544 discloses a threaded pipe connection with tapered stepped threads on ends of the connected tubular and a seal between the stepped threads. Wedge threads are shown in FIG. 1 of the '544 Patent and hook threads as shown in FIG. 4.
U.S. Pat. No. 4,703,954 discloses a pipe connection with wedge threads as shown in FIG. 4 and a seal between the wedge threads.
Threaded pipe connections are being increasingly used in applications which require that the threads transmit very high torque, e.g., when rotating liners, a torque of 50,000 foot pounds or more must be transferred through he threaded connection in some applications. Many threads are also susceptible to galling, are difficult to make up, require the use of a special (non-API) coupling, or are not capable of reliably transmitting the various loads to the connection.
The disadvantages of the prior art are overcome by the present invention, an improved thread pipe connection having tapered stepped threads is hereinafter disclosed.